The reliability and quality of a computer system depends on properly protecting hardware components of the computer system against power disturbances. Power disturbances can be divided into several categories. Noise or static is a minor disturbance characterized by a small change in voltage. A transient, sometimes called a spike or surge, is a disturbance characterized by a very short, but extreme burst of voltage. Brownouts and blackouts are severe disturbances characterized by the temporary drop and complete loss of electric power, respectively.
Of these disturbances, blackouts pose a serious threat to today's computer systems, which heavily rely on volatile memory components that are particularly susceptible to power interruptions. Prior to shutting down a computer system, it is important to ensure that no portion or segment of the system is in a condition of instability. In a blackout, a complete power interruption causes the instant shutdown of a computer system thereby disrupting and destabilizing the transfer and storage of data. The data may be lost or corrupted or placed in an unpredictable form.
Computer systems have been designed to avoid power interruptions and to maintain extended availability or “uptime.” To extend availability, computer systems can include uninterrupted power supplies (UPSs) that are typically equipped with a battery and a loss-of-power sensor. When the UPS detects a power failure, it switches to battery power so that the computer system may remain operational. If power does not resume, the UPS may send a power loss notification to the computer system so that an orderly and graceful shutdown of the computer system can be performed. However, some power failures may not affect all components of a system and shutting down the entire system may not be necessary.